The present invention relates generally to a spinal fixation and retrieval device, and more particularly to a spinal fixation and retrieval device capable of providing micromotion.
The conventional spinal fixation and retrieval device contains a rigid bone plate and bone nails, which is implanted in the body of a patient under spinal treatment with the bone nails and the bone plate being intimately joined together. In light of the intervertebral distance being caused to shorten by the body weight of the patient in the wake of surgery, the bone plate and bone nails are susceptible to falling apart. The bone nails are even vulnerable to severance. In addition, all the bone nails fastened onto the bone plate are prone to be affected, when one bone nail is out of order. As shown in FIGS. 1a, and 1b, the prior art device comprises a bone plate 100xe2x80x2 and a plurality of screws 200xe2x80x2. FIG. 1a shows a schematic view taken immediately after the surgery. FIG. 1b is a side view of FIG. 1a. The prior art device is implanted into the spinal segments 600 and 650. The letter xe2x80x9cDxe2x80x9d denotes the distance between the two spinal segments 600 and 650. Immediately after the surgery, the bone nails 200xe2x80x2, the spinal segments 600 and 650, and the bone plate 100xe2x80x2 are intimately joined together such that the threaded stems 280 are parallel to each other. FIGS. 1c and 1d are schematic views taken in a period after the surgery. As shown in FIG. 1c, the distance xe2x80x9cdxe2x80x9d becomes smaller, due to the body eight of the patient. As shown in FIG. 1d, the threaded stems 280 are no longer parallel to each other; they form therebetween an acute angle. As a result, the bone nails 200xe2x80x2 are apt to become unfastened. A crack or severance may occur in the necks 220xe2x80x2 of the bone nails 200xe2x80x2.
With a view to providing a solution to the problem described above, this inventor of the present invention disclosed a drawer-type vertebral auxiliary fixation device capable of providing micromotion in U.S. Pat. No. 5,616,142. However, this drawer-type device is by no means free of deficiency. For example, the drawer-type device can not be easily bent to conform to the spinal curvature. In addition, the structural strength of the drawer-type device is often inadequate unless the device has an appropriate height. Moreover, the drawer-type device does not have a supporting force at the time when the surgery is completed.
It is therefore the primary objective of the present invention to provide a spinal fixation and retrieval device which is free of the drawbacks of the prior art devices described above.
In keeping with the principle of the present invention, the foregoing objective of the present invention is attained by the spinal fixation and retrieval device comprising:
a bone plate having a plurality of slot holes; and
a plurality of screws, said screws being fastened via said slot holes onto vertebrae under treatment, at least one of which has a head, a threaded stem, and a neck connecting said head and said threaded stem;
wherein at least one of said plurality of slot holes is a long slot hole provided with a protruded edge at a bottom of each of two opposite walls defining a width thereof; wherein said head has a diameter ranging between said width of said long slot hole and a distance between said protruded edges.
Preferably, said long slot hole is slanted outward from said bottom to an upper portion thereof.
Preferably, said neck has a diameter smaller than said distance between said protruded edges.
Preferably, said threaded stem comprise a first spiral ridge adjacent to said neck having a diameter greater than said distance between said protruded edges and a shank next to said first spiral ridge having a diameter smaller than said distance between said protruded edges. More preferably, said first spiral ridge has the greatest diameter in said threaded stem.
Preferably, said protruded edges has a thickness substantially smaller than a pitch between said first spiral ridge and a second spiral ridge next to said first spiral ridge.
The present invention also provides a spinal fixation and retrieval device comprising:
a bone plate having a plurality of slot holes; and
a plurality of screws, said screws being fastened via said slot holes onto vertebrae, at least one of which has a head, a threaded stem, and a neck connecting said head and said threaded stem;
wherein at least one of said slot holes is a long slot hole having two opposite walls defining a width of said long slot hole, and said two opposite walls further being slanted outward from a bottom portion to an upper portion thereof; wherein said head has a diameter ranging between a relatively longer distance between said upper portions and a relatively shorter distance between said bottom portions of said two opposite walls.
Preferably, said neck has a diameter smaller than said relatively shorter distance between said bottom portion of said two opposite walls.
Preferably, said threaded stem comprise a first spiral ridge adjacent to said neck having a diameter greater than said relatively shorter distance between said bottom portions of said two opposite walls and a shank next to said first spiral ridge having a diameter smaller than said relatively shorter distance between said bottom portions of said two opposite walls. More preferably, said bottom portions of said two opposite walls have a thickness substantially smaller than a pitch between said first spiral ridge and a second spiral ridge next to said first spiral ridge.